1. Field of the Disclosure
This disclosure relates to an actuation mechanism for the adjustment ring of a variable turbine geometry turbocharger. More particularly, this disclosure relates to a gear driven adjustment ring to adjust the turbine vanes in a variable turbine geometry turbocharger and to a resiliently mounted actuation mechanism for the adjustment ring in the variable turbine geometry turbocharger.
2. Description of Related Art
A turbocharger is a type of forced induction system used with internal combustion engines. Turbochargers deliver compressed air to an engine intake, allowing more fuel to be combusted, thus boosting the horsepower of the engine without significantly increasing engine weight. Turbochargers allow for the use of smaller engines having the same amount of horsepower as larger, normally aspirated engines. The use of a smaller engine in a vehicle decreases the mass of the vehicle, increases performance, and enhances fuel economy. Moreover, turbochargers provide a more complete combustion of the fuel delivered to the engine, which contributes to the highly desirable goal of a cleaner environment.
Turbochargers typically include a turbine housing connected to the exhaust manifold of the engine, a compressor housing connected to the intake manifold of the engine, and a center bearing housing coupled between the turbine and compressor housings. A turbine wheel in the turbine housing is rotatably driven by an inflow of exhaust gas supplied from the exhaust manifold. A shaft rotatably supported in the center bearing housing connects the turbine wheel to a compressor impeller in the compressor housing so that rotation of the turbine wheel causes rotation of the compressor impeller. The shaft connecting the turbine wheel and the compressor impeller defines an axis of rotation. As the compressor impeller rotates, it increases the air mass flow rate, airflow density and air pressure delivered to cylinders of the engine via the intake manifold.
A turbocharger provides an ideal boost in only a limited range of conditions. Thus, a larger turbine for a given engine provides good boost at high speeds, but does not do well at low speeds because it suffers turbo lag and is thus unable to provide boost when needed. A small turbine provides good boost at low speeds, but can choke the engine at high speeds. One solution to this problem is to provide the turbocharger with a variable geometry turbine (VGT) having movable vanes in the turbine housing. At low speeds, when boost is needed quickly, the vanes can be closed creating a narrower passage for the flow of exhaust gas. The narrow passage accelerates the exhaust gas towards the turbine wheel blades allowing the turbocharger to provide a boost of power to the engine when needed. On the other hand when the engine is running at high speed and the pressure of the exhaust gas is high, the vanes may be opened and the turbocharger provides the appropriate amount of boost to the engine for the associated speed. By allowing the vanes to open and close, the turbocharger is permitted to operate under a wide variety of driving conditions as power is demanded by the engine. As such, the vanes are frequently adjusted using an adjustment ring mechanism. The vanes are attached to a shaft which is in turn attached to vane arms that engage pins disposed on an adjustment ring. Thus, the position of each vane is adjusted in unison with the other vanes as the adjustment ring is rotated. The adjustment ring is driven by an actuator, and is connected to the actuator by various mechanical drive linkages well known in the art. Unfortunately, some currently available linkages are imprecise and suffer from hysteresis.